The invention relates to a cooler for cooling hot bulk material according to the preamble to claim 1 and also to a method of cooling hot bulk material according to the generic concept of claim 9.
For cooling of hot bulk material, such as for example cement clinker, the bulk material is fed on a cooler grate through which cooling air flows. During transport from the start of the cooler to the, end of the cooler, cooling air flows through the bulk material thereby cooling it.
Various possibilities are known for the transport of the bulk material. In the so-called reciprocating grate cooler the bulk material is transported by movable rows of cooler grates which alternate with stationary rows of cooler grates in the direction of transport.
It is also known to provide a stationary aerating base, through which cooling gas can flow, in order to receive the bulk material, with conveyor elements for transport of the bulk material above the aerating base. In the transport mechanism there is a distinction between rotating conveyor elements and reciprocating conveyor elements.
A cooler according to the preamble to claim 1 is known from DE 878 625. The conveyor elements described there are formed by bars which are disposed above a stationary grate and extend in the longitudinal direction parallel to the plane of the grate. The bars are connected to a suitable moving mechanism which makes possible a reciprocating movement of the bulk material in the transport direction. In addition, suitable projections are provided on the bars in order to assist the conveying action.
In contrast to the rotating conveyor elements, in the case of the reciprocating conveyor elements the problem arises that some of the bulk material is carried back with the return stroke. However, this disadvantage can be compensated for by a suitable design of the conveyor elements. Thus for example conveyor-elements are proposed with a substantially triangular cross-sectional shape, in which the end face pointing in the transport direction is substantially perpendicular to the transport direction and the rear end face encloses an angle between 20 and 45xc2x0 with the aerating base. Whereas in the forward stroke the substantially perpendicular end face achieves a good conveying action, in the return stroke the conveyor element can be drawn back under the bulk material due to its wedge shape.
Also with such a construction of the conveyor elements some of the quantity of bulk material is carried along with the return stroke.
The object of the invention, therefore, is to improve the cooler according to the preamble to claim 1 or the method according to the generic concept of claim 9 with regard to the conveying action.
This object is achieved according to the invention by the features of claims 1 and 9.
Further embodiments of the invention are the subject matter of the subordinate claims.
The cooler according to the invention for cooling hot bulk material has a stationary aerating base, through which cooling gas can flow, in order to receive the bulk material and also has reciprocating conveyor elements disposed above the aerating base for transport of the bulk material. The conveyor elements are provided in at least two groups which can be actuated jointly in the transport direction of the bulk material and separately from one another against the transport direction.
Particularly in the case of coarse bulk material, the bulk material forms a relatively compact unit which can be moved with the joint forward stroke of the conveyor elements in the transport direction. As the various groups of conveyor elements are actuated individually and successively with the return stroke, because of the friction conditions in the material bed considerably less bulk material is carried along against the transport direction than in the case of a joint return of all conveyor elements.
Each group of conveyor elements consists of at least one conveyor element or conveyor element line.
In a further embodiment of the invention it is also conceivable that the conveyor elements of a group can be actuated individually, so that they can be actuated for example at different speeds and for different lengths of time or with different strokes.
In a first embodiment the individual groups of conveyor elements are provided so that they alternate transversely with respect to the transport direction of the bulk material. In the tests on which the invention is based it has been shown that the best results can be achieved with three groups of conveyor elements which are disposed so that they alternate transversely with respect to the transport direction.
In a second embodiment the conveyor elements which are adjacent transversely with respect to the transport direction are disposed in such a way that at each phase of the sequence of movements they are oriented offset from one another in the transport direction.
In a third embodiment according to the invention the individual groups of conveyor elements are disposed so that they alternate in the transport direction of the bulk material.
Because of the friction conditions in the region of the lateral limits of the cooler or for reasons related to process engineering it may be advantageous to design the stroke of the conveyor elements to be of differing length over the width of the aerating base.
Further advantages and embodiments of the invention are explained in greater detail with reference to the description of some embodiments and the drawings.